Various techniques and apparatus are known for measuring, and for detecting changes in, intrapleural pressure of a human subject or other living organism. Present techniques are invasive in requiring that at least some portion of a device be inserted into the body as, for example, directly into the pleural or adjacent esophageal space. The most commonly used such device, the esophageal balloon, is based upon the known close correspondence between esophageal and intrapleural pressures. Although the esophageal balloon is perhaps the least objectionable of the available invasive devices with respect to subject discomfort and acceptance, it cannot be used for intrapleural pressure monitoring over extended periods of time and it is particularly difficult to successfully maintain in situ when dealing with newborn subjects. In addition, it has recently been suggested that distortion of the rib cage of preterm and term infants during breathing invalidates the use of esophageal pressure as an estimate of mean pleural pressure.
Maintaining a monitoring probe or device on or about an infant's body is frequently difficult to achieve and applicant is unaware of any prior art technique or device that can be conveniently and noninvasively utilized to continuously monitor intrapleural pressure in a newborn.
Prior art methods and apparatus known for monitoring a newborn to detect the presence of apnea may be designed to sense body movements, as by a detector underlying the subject's mattress during sleep. This method has inherent unreliability since any normal change in body position during sleep can introduce substantial variations into the signal generated by the sensor in response to respiration-related body movements. In addition, such techniques fail to provide a reliable means by which the apnea can be readily differentiated as being either central or obstructive in origin. Immediate differentiation is important in that while central apnea is often treated with drugs, obstructive apnea requires mechanical relief of airway obstruction and, in either event, the appropriate procedure or countermeasure must be introduced at once to restore normal respiration. Even a relatively short delay required to separately diagnose the problem can prove fatal to the newborn. External monitoring devices worn around the rib cage and abdomen, such as magnetimeters, respiratory inductive plethysmographs, and impedance pneumographs may detect central apneas but if respiratory efforts are minimal (i.e. where changes in intrapleural pressure are small) then obstructive apneas may not be diagnosed. Further, if external monitors such as the impedance pneumograph are worn over only the rib cage and abdomen, obstructive apneas will not be diagnosed if respiratory efforts are present. Finally, devices sensing air flow at the nose, such as thermocouples, thermistors and CO.sub.2 analyzers will detect apneas but fail to differentiate central from the obstructive types.